Fire box construction



1 mg. 1, 1933.. M VAN WQERT E,92,8fi7

FIRE BOX CONSTRUCTION Filed Dec. 6. 1929 2 Sheets-Sheet l INV QMM ZMATTORNEYS 3- M. P. VAN WOERT 1,920,817

FIRE BOX CONSTRUCTION Filed Dec. 6, 1929 2 Sheets-Sheet 2 CID BUD um umum 28 3/ uu'uoun uuunuunun 2 Z uuouuuunuu EIEI UDEID 30 uunuuuuuun an 004/ /48 lNVE 10 ATTORN EY5 Patented Aug. 1, 1933 I 1,920,817 FIRE BOXCONSTRUCTIQN Application December 6, 1929. Serial No. 412,115

rarest easier 7 Claims.

This invention relates to furnace grates and is concerned moreparticularly with a grate construction especially adapted for heavy dutyuse as in locomotives, marine boilers and the like.

In locomotive fire-boxes, the grate extends the full length of thefire-box and below the grate is an ash pan with openings along the sidesof the fire-box through which air is admitted beneath the grate. Abovethe grate is the usual brick 10 arch supportedon water tubes and thereis an opening through the arch near the front end of the fire-boxthrough which the gases of combustion pass on their Way to the firetubes, the area of the exit opening being relatively small compared tothe area of the grate. As the'opening lies above one end of the grate,the draft exerts its greatest pull on the fuel bed beneath or near theopening. If a fuel bed of uniform thickness from end to end and fromside to side 29 is maintained on the grate, a greater amount of air isdrawn through that portion of the fuel bed near the exit opening and alesser amount through the remainder of the bed, little air passingthrough the grate at the end remote from the exit opening. Similarlymore air passes through the sides of the fuel bed adjacent the lateralair admission openings than through the middle and this unevendistribution of air causes inefficient combustion and poor operatingcondi- 30 tions. The fuel at the end of the grate near the exit openingburns rapidly While that at a distance from the opening is consumedslowly and possibly with insufficient air forcombustion. A r similaruneven distribution of air occurs with respect to the side portions ofthe fuel bed and the portion which lies along the middle of the grate.In order to overcome these difficulties, the fireman ordinarily tries tomaintain a relatively thick bed of fuel on the grate near the fire doorand a thinner layer further back and beyond the rear edge of the exitopening through the arch. Similarly, he tries to keep a thicker layeralong the sides of the grate than at the middle. This expedient,however, is unsatisfactory since in order to approximate an evendistribution of the air to the fuel in this manner, the fuel bed isusually maintained at such a thickness near the fire door and along thesides that the fire burns sluggishly on this part of the grate an islikely to be choked with ashes. Also, it'is extremely difficult forthefireman to, attain a distribution of the fuel which will result ineven a close approach to ideal conditions.

In Scotch marine boilers, the same difficulties are encountered thoughin the fire-boxes of such boilers, the exit opening for the gasesliesabove the top of a bridge wall at the rear. end of the grate. Herethe greatest pull of the draft is' on that part of the fuel bed nearestthe bridge wall and on this part of the grate the deepest bed of fuel isusually maintained with a relatively thinner bed elsewhere.

The present invention is directed to the provision of a grate in whichthe difficulties above mentioned are overcome and on this grate a bed offuel of uniform depth may be maintained from one end to the other andfrom side to side regardless of the differences of the pull of the drafton different portions of the'fuel bed. The grate is so constructed as toinsure a thorough distribution of the air to all parts of the fuel bed,and the flow of air through the fuel on those parts of the grate wherethe pull of the draft is greatest is restricted to compensate for thedecreased pull through the fuel on other portions of the grate. Withthis construction, the entire fuel bed burns at a substantially uniformrate and good combustion is obtained throughout, this result beingdependent only to a slight degree on the skill of the fireman.

For a better understanding of the invention, reference may be made tothe accompanying drawings, in which 7 Fig. 1 is a longitudinal sectionalView through a locomotive fire-box showing the grate of the presentinvention;

Fig. 2 is a longitudinal section through a boiler of the Scotch marinetype showing the application of the new grate;

Fig. 3 is a view illustrating one type of grate bar used in the newgrate and showing the supporting member in section and a cross-bar inelevation;

Fig. l is a fragmentary plan view of a portion of the grate made up ofthe bars illustrated in Fig. 3;

Fig. 5 is a fragmentary plan View illustrating a portion of the grateconstructed in accordance with my invention;

Fig. 6 is a view similar to Fig. 3 showing a different type of baruseful in the new grate; and

Fi '7 is a plan view of a portion of a grate bar which may be used inpractising the invention.

Referring now to the drawings, the new grate fuel with a fuel bed ofuniform thickness.

air.

customary elongated form and extending lengthwise of it are water tubes11 on which are mounted fire brick 12 forming the usual arch. This archextends from the rear end of the fire-box to a point near the front endat which the fire door 13 is located, the front edge of the brick beingspaced from the front Wall of the fire-box to form an exit opening forthe gases. The grate consists of a plurality of bars 14 extending acrossthe fire-box from side to side, these bars being of the shaker type andmounted on trunnions in a suitable supporting frame. In a largefire-box, there will be two rows of such grate bars, the trunnions atthe outer ends of the bars of the two rows beingsupported in a suitableframe member at the sides of the fire-box and the trunnions at the innerends of the bars being supported in a suitable frame member extendinglengthwise of the fire-box along its median line. The bars are providedwith individual shaker arms 15 connected by a shaker rod 16 which leadsto a point at the front of the fire-box where it is connected to ashaker handle, not shown.

In a fire-box of this construction, it will be seen that the exitopening for the gases of combustion through the arch is of much lesssize than the area of the grate and it lies over the front end of thegrate. Accordingly, the draft exerts its greatest pull on the fuel bedsupported on that portion of the grate which lies nearest the opening,that is, on grate bars which lie directly beneath the opening. The pullof the draft on the bed of fuel on the grate bars at the rear end of thefire-box beneath the arch is relatively less and the pull increases asthe opening is approached. Similarly, since the air flows into the spacebeneath the grate through openings, one on each side of the fire-box,more air flows through the grate along the sides of the fire-box than atthe middle.

Grate bars of standard constructionhave air openings therethrough forthe passage of air to the fuel and in the ordinary grate the bars areall alike so that the total cross-sectional area of the openings perunit of grate area is the same regardless of where the unit is locatedin the grate. In a standard grate bar the combined areas of the airopenings is equal to approximately 50% of the total top area of the bar.The remainder of the top area of the bar is solid metal and consists ofa fuel-supporting surface. In such a bar, the area of the total fue1supporting surface varies inversely with the combined areas of'the airopenings and, while in some bars used, for example, for burning ligniteor similar fuels, fewer openings are provided than is customary forother fuels, the decrease in the combined areas of the air openingsresults in an increase in the total fuel-supporting surface.

In a grate of standard construction used in a fire-box of the typeillustrated in Fig. 1, it is not possible to obtain good combustion ofthe This is due to the variation in the pull of the draft on differentparts of the fuel bed. The fuel on that part of the grate which liesnearest the exit opening may receive an amount of air which is in excessof that required for good combustion,

while the fuel on other portions of the grate more remote from the exitopening receives less The fuel on that part of the grate which liesdirectly beneath the exit opening, therefore,

. burns .more rapidly and the burning gases are drawn into the firetubes 18 and are likely to pass out the stack before they are completelyconsumed. The fuel on a bar, such as that designated 19, which is remotefrom the opening, is supplied with less air than is desirable and thefuel consequently burns sluggishly.

In order to overcome the non-uniform combustion conditions in differentparts of the fuel bed on a standard grate as above described, it is thepractice to maintain a bed of fuel of greater depth on that part of thegrate which 'lies adjacent the exit opening, the thickness of the bed offuel on this part of the grate being indicated by the broken line A.Similarly the deeper bed of fuel is maintained along the sides of thefire-box than in the middle. Such a fuel bed is maintained on the gratein the hope that the increased resistance to flow of air through thedeeper part of the bed will overcome the increased pull of the draftthereon, to the end that substantially the same volume of air will passthrough a unit area of the grate regardless of where the area islocated. In actual practice, this result is not obtained but, on thecontrary, the thick burning mass on those parts of the grate near theexit opening and along the sides is likely to become choked with ashes,so that ideal conditions are by no means closely approached. A skillfulfireman will perhaps obtain better results than one of less ability, butunder any circumstances, the difficulty of firing and maintaining a bedof fuel of the proper graduated thickness from one end of the grate tothe other causes faulty combustion and waste of fuel.

In a boiler of the Scotch marine type such as that illustrated in Fig.2, the exit opening for the gases is defined in part by a bridge wall 19and the greatest pull of the draft is exerted on the fuel nearest thebridge wall, so that a greater amount of air than is required issupplied to that portion of the fuel bed, while the fuel at a distancefrom the bridge wall receives substantially less air. Here again inpractice, the fireman attempts to maintain a thick bed of fuel of thedepth indicated at the broken line B on that part of the grate which isnearest the bridge wall, but,'as is the case inthe locomotive boiler,this expedient is at best only a make-shift.

In order to overcome these difficulties, I have devised a grate which ismade up of a plurality of individual bars having fuel supportingsurfaces and openings for the passage of air, and the openings in thebars nearest the exit opening are smaller in size than the openings inbars disposed at a distance from the exit opening. Similarly, ifdesired, the openings through the ends of the bars adjacent the sides ofthe fire-box are smaller in size than those in portions of the barswhich lie spaced from the sides of the fire-box. Since the bars are sodisposed that the smaller openings lie where the pull of the draft isgreatest, the amount of air supplied to the fuel may be madesubstantially uniform throughout the fire-box.

While a grate embodying the principles of this invention may be made ofbars of numerous kinds, I prefer to employ the bar shown in theco-pending applications of Buckley, Serial No. 338,352, filed February8, 1929, and of Thompson, Serial No..406,558, filed Nov. 12, 1929. Thebar of the Buckley appli ation includes a supporting member 20 providedat its ends with trunnions 21 and on this member are mounted a pluralityof cross-bars 22, each of which is formed with spaced lugs 23 on itsopposite faces: Extending upwardly from the tops of the bars aretapering projections 24, these projections having flat tops which serveas fuel-supporting surfaces. Adjacent lugs on thecross-bars define airpassages 25 and these lugsare preferably of increasing width from bottomto top so that the effective cross-sectional area of each passage is .inpart determined by the distance between adjacent lugs at the point 26.The projections are preferablyformed in groups of four, as indicated inFig. 4, and in each group of projections, such as that designated 27,the projections 28 may lie above the top of a lug, while the projections29 may lie above the main body of the cross-bar adjacent this lug. Theprojections of each group are separated by intersecting channels 30 and31 and there is a central channel 32 extending along the top of across-bar between groups of projections. The cross-bars on thesupporting member 20 are separated-to form an air space 33 between them,the amount of separation being determined by spacing projections 34 oncertain of the lugs 23. Y

The bars are mounted side by side'with their trunnions received insuitable sockets in a frame and there is a space 35 between the ends ofaligned cross-bars on adjacent supporting members, as illustrated inFig. 4. With this arrangement, the fuel is supported on the tops of theprojections 24 and is supplied with air which passes up through thespaces 33 and 35 and through the passages 25. The air enters the severalchannels 30, 31, and 32 and flows around the projections so that itreaches all parts of the fuel except such as are directly in contactwith the tops of the projections. As these projections are of relativelysmall area, there is little dead space at the bottom of the fuel bedwhere air cannot reach the fuel.

In one form of grate constructed in accordance with the invention oi theBuckley application, the top of'each projection may be one-quarter inchon each side, each cross-bar carrying 96 projections, with 18 cross-barson each supporting member. The dimensions of the outline of the top ofthe grate may be 12" by 36 and the width'of the spaces between adjacentcrossbars on the same bar and between the ends of aligned cross-bars onadjacent supporting members may be one-quarter inch. In a grate bar ofthe dimensions specified, the aggregate area of the tops of theprojections is about 25% of the total top area ofthe bar and the totalair space area including the space between adjacent cross-bars on onesupporting member and be tween the ends of aligned cross-bars onadjacent supporting members is in the vicinity of 30% of the total toparea of a single bar. The total fuel supporting area and total air spacearea of this grate are, therefore, both substantially less than thecorresponding values in a standard grate bar where the total air spacearea approximates 50% of the total top area of the grate. However, ithas been found that better combustion results are obtained with a gratemade of bars of this type than of standard bars, even though less air isconducted through the grate to the fuel, this result being obtainedbecause of the superior distribution of air and the elimination of deadspace on the bottom of the fuel bed.

A bar of the type illustrated in Fig. 3 may be used in such portions ofthe new grate as lie remote from the exit opening, while the bars usedinthat part of the grate nearthe exit opening aresimilar in constructionbut the lugs on the cross-bars are larger so as-to reduce the size ofthe passages between them and thus reduce the amount of .air flowingthrough the grate bar. By the use of suitable patterns, grate bars maybe made giving the desired air flow for different parts of the grate-The grate bar illustrated in Fig. 6 is of the Thompson type and includesa carrier member 20 and a plurality of cross-bars 22 mounted thereon.Each cross-bar is made with a plurality of spaced lugs 23 on itsopposite faces, but the top of the cross-bar and the tops of the lugsare provided with channels 23"which subdivide'the top of the cross-barand lugs into a plurality of smaller fuel supporting surfaces on allsides of which the air is free to flow. In the Thompson bar, the airpassages 25 between adjacent lugs are of decreasing cross section frombottom to top and the channels 23 communicate with the air passagesbelow the point of maximum restriction thereof. The tops of the passagesconstitute orifices at which an eifective pressure drop takes place andat the points where the channels 23 communicate with the air passages,minor orifices are formed at which a pressure drop occurs. As aconsequence of this construction, the air drawn up through the grate bythe pull of the draft increases in velocity as it approaches the top ofthe grate and the air is discharged from the grate through orifices sodisposed that the air enters the fuel bed supported on the grate at highvelocity 1 and with a wide distribution.

In constructing the new grate of either type of bar above described, itwould be desirable theoretically to form each bar with air passages ofdifferent sizes, the bars nearest the exit opening having the smallestportion and the crosssectional area of the passages increasing with thedistance of the bars from the exit opening. Similarly, it would bedesirable to. construct each bar with openings of greater size in thoseparts of the bar which lie near the air admission openings alongthesides of the fire-box. It is possible with the grate bar as abovedescribed toobtain this desirable result, since each grate baris made upof a plurality of crossbars which are detachable therefrom so thatcross-bars of different constructions providing different air passagesmaybe mounted on the single carrier bar. As a practical matter, it isusually sufficient to form the grate of two groups of bars, the firstgroup lying near the opening and having air passages about half the sizeof those through the bars of the second group which lie farther from theexit opening. Similarly, each bar may be madeup of a carrier member andcross-bars of two different kinds, those cross-bars which lie on thecarrier member adjacent the air admission openings'defin ing smaller airpassages than the cross-bars which lie on the carrier bar near themiddle of the fire-box. 'Due to the excellent air distribution which isobtained with the bars ofthe construction described by reason of thefuel-supporting surface being sub-divided into a multiplicity of smallareas, excellent results are obtained from a grate made up of the barsof the two kinds mentioned. i

In Fig. 7 there is illustrated in plan view a portion of a grate barmade up of cross-bars of different types. The cross-bar 35 is placed onthe carrier member20 adjacent the side of the fire-box and it will beobserved" that the air 1 It will be apparent, thereforefthat the new andfrom side to side. It is not necessary for passage 36 between'adja'centlugs on the. crossbar is relatively small. The cross-bar 37 is similarin construction to the cross-bar 35 and they two'cross-bars are spacedapart'on the carrier member to define a relatively narrow. air passage38 between the ends of opposed lugs. The crossbars 39 have lugsspacedapart to define air passages 40 between them which are wider than thepassages 36, and these cross-bars are spaced from the nextcross-bar 39to define an air passage 41 which is wider than the air passage 38; Bythis arrangementthe pull of the draft on the cross-bars 35 and 37produces a flow of air which is about the vsame as that drawn throughthe passages defined by cross-bars 39. As a consequence, auniform bed offuel may be maintained on the grate bar of which cross-bars 35,37 and 39form a partand all parts of the fuel receive air in proper amounts forcombustion.

In Fig. 5, there is illustrated a portion of the grate includingportions of a pair of grate bars near one end of the fire box andportionsof another pair of grate bars near the other end of the firebox. The grate bars near one end have cross bars 41 having lugs 42defining air passages 43 between them, certain of the lugs havingspacing lugs 44. The I cross bars of adjacent grate bars define an airpassage 45' between their ends. The cross bars 41 have relatively largelugs 42 defining relatively small air passages 43 and the spacing lugs44 are of a size such that the air passage 46 between adjacent crossbars of a single grate bar is relatively small. Also, the crossbars areof .a length such that the passage between the ends of cross bars of twoadjacent grate bars is relativelysmall.

At the other end of the fire box, the grate bars have cross bars 47provided with lugs 48 smaller l than the lugs-42".and defining. airpassages 49 larger than the passages 43. Also, the spacing lugs 50 arelarger than the lugs 44 so as toprovide air passages 51 between adjacentcross bars which are larger than theair passages 46. Also,

3 the cross bars 47 areslightly shorter than the cross bars 42, thusproviding air passages 52 between the ends of cross bars of adjacentgrate bars which are larger than the air passages 45. With thisarrangement, more air will pass through the grate in those areas wherecross bars 47 are employed than throughrthose areas where bars 41 areused. Cross bars 41 willbe employed near the exit openings and crossbars 47 farther from the exit openings. I

In the newgrate, variations in the flow of air through the grate barsnear and. more remote from the exit opening, due to-the varying effectof the pull of the draft, are compensated for by employing cross-bars ofappropriate dimensions.

grate may be so constructed that substantially uniform air fiow takesplace therethrough and as a consequence, the fireman may maintain. a

bed of fuel of uniform thickness from end to end the fireman to attemptto equalize the pull of the draft by varying the thickness of the fuelbed on different parts of the grate, firing is simplified and betterresults are obtained. In some fire boxes, grate barsin two groups ofvarying of bars in a grate, particularly whenthe bars are of theThompson and Buckley types, due to the excellent air distributionthroughout the bed of fuel which is obtained by bars of thoseconstructions.

. It will be apparent that in the type of fire-box illustrated in Fig.2, those bars which lie nearest to the bridge wall will have the smallerair openings, while the bars more remote from the bridge wall will havethe larger ones.

What I claim is:

1. In a fire-box having an exit opening for gases of combustion, a gratemade up of a plurality of individual grate bars, each of which has afuel-supporting surface made up of a plurality of minor areas and also aplurality of openings for the passage of air around all sides of saidminor areas, the aggreate areas of the fuel-supporting surfaces of theseveral bars being the same, with the aggregate areas of the airopenings in a unit of grate surface adjacent the exit opening being lessthan those in a unit of grate surface more remote from said exit openingin a direction lengthwise of the grate.

2. In a fire-box having air admission openings along its sides and nearthe bottom thereof, a grate made up of a plurality of individual gratebars extending transversely of said firebox, said bar being spaced apartand providing air openings between parts thereof and between adjacentbars, the total area of the openings per unit of grate area beinggreater at the middle of the grate than along the sides adjacent the airopenings in said ash pan.

3. In a fire-box having an exit opening, a grate made up of a pluralityof individual grate bars extending transversely of said fire-box, saidbars being spaced apart and providing air openings between parts thereofand between adjacent bars, the total area of the openings per unit ofgrate area increasing with the remoteness of said unit from said exitopening and also from the lateral sides of said fire-box.

4. In a fire-box having an exit opening, a grate made up of a pluralityof grate bars, each of which includes a carrier member and cross barsmounted thereon, said cross bars having lugs on their opposite facesdefining air passages. the cross-bars near said exit opening havingrelatively large lugs and being spaced close together on said supportingmember to permit a restricted flow of air to the fuel supported thereonand said cross bars remote from said exit opening having smaller lugsand being spaced relatively far apart to permit a greater volume of airto pass to the fuel supported thereon.

5. In a fire box having an exit opening for gases of combustion, a gratemade up of a plurality of individual grate bars extending across thefire box, each bar providing a plurality of passages for air within theoutlines thereof and adjacent bars being spaced to provide air passagesbetween them, the total cross-sectional area of said passages in a'unitof grate surface increasing with the remoteness of said unit from theexit opening.

.6. In a fire box having an exit opening, a grate made up of separategrate bars providing fuel supporting areas and passages for air, thetotal fuel-supporting area per unit of grate surface being substantiallyconstant throughout the fire box, and the total cross-sectional area ofthe air passages differing in different units of grate surface andincreasing with the remoteness of said units from the exit opening.

7. In a fire box having an exit opening at one end and near its top andair admission openings along its sides near its bottom, a grate betweenthe admission openings and. exit opening and made up of individual gratebars, each providing fuel-supperting areas and passages for air, thetotal cross-sectional area of the air passages per unit of grate surfaceincreasing with MYRON P. VAN WOERT.

